Field of the Invention
The present disclosure relates to a process and an apparatus for forming graphene, and in particular to a process and apparatus for forming a graphene layer by chemical vapor deposition.
Description of the Related Art
Graphene is a substance composed of carbon atoms forming a crystal lattice one atom in thickness. Various applications have been proposed for graphene, including its use in radio-frequency transistors and for forming transparent highly conductive and flexible electrodes, such as for displays. It is of particular benefit in applications where high mobility conductors are desired. Most applications of graphene require a macroscale-sized graphene layer, comprising one or a few layers of carbon atoms, which is transferred onto a substrate of a material selected based on the particular application.
One solution for forming such a macroscale-sized graphene layer is to use chemical vapor deposition (CVD). For example, a process based on this technique in which graphene is formed on copper foil is described in U.S. patent application US2011/091647. One problem with this technique is that the quality of the graphene layer is heavily dependent on the quality of the copper foil.
On the one hand, use of a high quality copper foil may result in a graphene layer of reasonable quality. For example, the publication titled “Epitaxial growth of large-area single-layer graphene over Cu(111)/Sapphire by atmospheric pressure CVD”, Hu et al., Carbon Vol. 50, 2012, pages 57-65, describes forming graphene on high quality copper. However, the cost of such high quality copper foil prevents the process being adopted on an industrial scale, and the lateral dimensions of the graphene sheets that can be produced are generally limited. Furthermore, it is generally not possible to reuse the copper foil, as in order to transfer of graphene layer onto another substrate, the copper foil is generally etched away.
On the other hand, when an industrial quality copper foil is used, the cost is relatively low, but the quality of the graphene layer tends to be poor, multilayer patches being a common occurrence.